//Ta Duc Viet
//Tinh tong N so nguyen duong dau tien
#include <iostream>
using namespace std;
int Tong ( int n){
	if ( n == 0) return 0;
	else return n + Tong ( n - 1);
}
int main()
{
	int n;
	cout << "Tinh tong n so nguyen duong dau tien." << endl;
	cout << "n = ";
	cin >> n;
	cout << "Tong " << n << " so nguyen duong dau tien la:" << Tong (n);
	cout << endl;
	system("pause");
	return 0;
}
